[0.85] fix + review r20348


git-svn-id: https://forge.indepnet.net/svn/glpi/branches/0.85-work@20350 35612d4c-9d10-0410-837c-bf9dd1be60d7
[0.85] compy visibility from parent if not set : see #4233


git-svn-id: https://forge.indepnet.net/svn/glpi/branches/0.85-work@20351 35612d4c-9d10-0410-837c-bf9dd1be60d7